Originally Posted by TyreToaster
if you have the impco 425 carbs single or twin you will never get it to run the correct mixtures. Especially with you having the larger cam probably 225/236 duration 530/560ish lift you will find it either lean as buggery up high or rich as buggery down low and becuse you motor will utilise the larger rev range you may not be happy with the end result.
If you want it to run right make good power and not melt your pistons try buying s/h gas research setup much better option than the single stage adjustable IMPCO.
P.S before all you impco owners start abusing me and telling me i know nothing I will mention that my very mild street clevo ran an IMPCO 425 and impco E converter which is the big boy and it was lean enough to melt the lot, off course I had to wind up the mixture which meant at idle it was burning your eyes.
S/H Twin Gas Research setup $800-$1000
New Impco 425's X2 $600 2X Impco Converters $300 you decide.
It isn't that difficult to get a good result from the hunble IMPCO.
My Clevo runs straight gas, is making good rear wheel HP and does not run overly rich on idle. It's all about balance and building the motor for the LPG application. Long duration exhaust camshaft, right compression- higher is not always better or more efficient-correct manifold plenum vacuum and a damned good dyno operator. Remember that the motor does all the sucking as there is no pump for LPG like on petrol cars.
Admitedly, the IMPCO does lean out and mine does at 5500 RPM so I just make sure that I do not REV it past that level.
The GRA system may be better, but I have heard that they are also difficult to tune and can be expensive to muck around with.........metering rods etc.
Either way, if you build it right.............you'll be right